Precision delivery methods for fabrication of microarrays, including DNA and other nucleic acid microarrays, antibody and other protein microarrays and the like, utilize one of two different approaches. One approach, represented by the Gene Chip processing of Affymetrix, utilizes photochemical processing adapted from semiconductor technology. Wafer masking techniques are used for serial deposition of desired reagents at predetermined locations on a surface. Due to the spatial specificity of the manufacturing process, photochemical processing has a high degree of accuracy and reproducibility. However, the process tends to be both inflexible and expensive, making it not useful for innovative, small-scale laboratory research purposes.
The other approach is printing, either impact printing or inkjet printing. While potentially offering flexibility and low cost, printing has serious drawbacks. For both impact and inkjet printing, minimum spot size and reliability are limitations. Only about 40,000 individual spots can be printed on a standard microscope slide, for example, with a spot size of 150 microns. Also, printing techniques tend to waste a large portion of material, generally more than seventy-five percent of the starting material. Further, impact printing requires frequent replacement of hollow pins which are used to draw up liquid and “print” the liquid on a slide.